Cross-system bug fixing propagation is frequent among sys- tems having similar characteristics, using a common frame- work, or, in general, systems with cloned source code frag- ments. While previous studies showed that clones tend to be properly maintained within a single system, very little is known about cross-system bug management. This paper describes an approach to mine explicitly doc- umented cross-system bug fixings, and to relate their oc- currences to social characteristics of contributors discussing through the project mailing lists—e.g., degree, betweenness, and brokerage—as well as to the contributors’ activity on source code. The paper reports results of an empirical study carried out on FreeBSD and OpenBSD kernels. The study shows that the phenomenon of cross-system bug fixing between these two projects occurs often, despite the limited overlap of contributors. The study also shows that cross-system bug fixings mainly involve contributors with the highest degree, betweenness and brokerage level, as well as contributors that change the source code more than others.